Solution polyaluminoxane compositions are condensation products generally prepared by the partial hydrolysis of an organic aluminum compound. They are known to be useful as co-catalysts that efficiently activate the transition metal compounds serving as primary catalysts in the producing of olefin polymers. Polymethylaluminoxane compositions in which trimethylaluminum is employed as a starting material organic aluminum compound are widely known to perform particularly well as co-catalysts. These compositions are normally handled in the form of solutions obtained by dissolution in aromatic hydrocarbon solvents such as toluene.
Polymethylaluminoxane compositions perform well as co-catalysts. However, they are normally handled in a state where a primary catalyst such as a metallocene compound and polymethylaluminoxane composition have been dissolved in a solvent. Thus, the morphology of the polymer that is produced cannot be controlled. Not only does handling of the polymer present problems, but there is also a drawback in that fouling due to adhesion of the polymer to the polymerization reactor or the like occurs quite readily.
To solve these problems, a method of preparing a supported solid polymethylaluminoxane composition—consisting of a polymethylaluminoxane composition supported on a solid inorganic support such as silica, alumina, or magnesium chloride—applying the same to slurry polymerization or gas phase polymerization has been proposed. Silica of which surface hydroxyl group amount is controlled is the most widely employed support among solid inorganic supports, and there are a number of examples of its use at the industrial level. Use of a polymer support such as polystyrene beads is also proposed.
The above silica support is known to deteriorate the performance of polymers by tending to remain on the polymer, being a cause of fish-eyes in forming a film, and the like. Solid polymethylaluminoxane compositions in which such supports have been employed are known to exhibit a greater drop in activity than in the polymerization activity in homogeneous polymerization. Accordingly, to solve these problems, to reduce the negative impact of the support on the polymer while retaining the merits of a promoter in the form of a polymethylaluminoxane composition in a solid state, there is a need to develop a solid polymethylaluminoxane composition which is highly active as competitive to homogeneous polymerization.
We proposed a solid polymethylaluminoxane composition in the form of relatively fine particles with a volume-based median diameter in the range of 5 to 50 μm, and comprising solely a polymethylaluminoxane composition without any support such as silica, along with a method for efficiently preparing these (PTL 1). The resulting solid polymethylaluminoxane composition has a relatively uniform particle diameter, and the polymerization activity when preparing an olefinic polymer is higher than that of a solid polymethylaluminoxane composition using a support. Depending on the polymerization conditions, it may express activity comparable to that of a solution polymethylaluminoxane composition. That is, the solid polymethylaluminoxane is a novel solid co-catalyst that combines the properties of a strong co-catalyst (activator) with the function of a support. Moreover, we also proposed a solid polymethylaluminoxane composition having a volume-based median diameter of less than 5 μm that is smaller than that of the polymethylaluminoxane composition described in PTL 1, as well as a particle size distribution with high homogeneity and strong polymerization activity when preparing an olefinic polymer, and reactor fouling suppression ability, along with a method for manufacturing the composition (PTL 2).
With the methods described in PTL 1 and 2 above, it is possible to provide methods that are highly efficient for preparing a solid polymethylaluminoxane composition from a solution polymethylaluminoxane composition, and do not require the solvent to be removed with a vacuum pump from the solution polymethylaluminoxane composition.
Patent Literature 1 (PLT1): WO2010/055652
Patent Literature 2 (PLT2): WO2013/146337
The entire contents of Patent Literatures 1 and 2 are incorporated herein particularly by reference.